The stock fuel system for the MR2 Turbo is capable of supporting roughly 280 crank hp. The fuel injectors are capable of delivering approximately 440cc/per minute of fuel at 37psi. The fuel pump is well matched to these injectors, and both the injectors and pump are limited to the same fueling level.
The MR2 Turbo was tuned very conservatively by Toyota to run very rich to reduce the likelihood of engine damage under high boost/engine speed conditions. By using an aftermarket fuel computer, such as the APEX’I S-AFC, can reduce the overabundance of fuel in the combustion chamber, picking up extra horsepower. Fuel tuning is dangerous business though, so it is highly recommended that you fuel tune your MR2 Turbo on an engine dyno for best results.
A common upgrade is to swap in the 550cc-fuel injectors and fuel pump from the latest generation Toyota Supra (1993-98). Combined these should support about 350 crank horsepower. The fuel pump resistor pack will need to be modified to handle the increased voltage utilized by the Supra’s fuel pump. A fuel computer, such as the APEX’I S-AFC, will also be required to control the injectors. Without such control the injectors will probably run much leaner than is necessary.
A common modification to the fuel rail is to convert it to a dual feed setup. The stock fuel rail is fed at the driver’s side end, which can lead to unequal fuel pressure across the fuel injectors. This can be dangerous to the engine at increased boost if one cylinder runs lean and causes detonation. The dual feed rail requires the owner to modify the rail to accept a second fuel entry point at the passenger side of the rail. This requires some drilling and tapping to allow for the second entry point. Often times this modification eliminates the cold start injector, which means the car will be more difficult to start and run when it is cold out.
The fuel filter should be changed every 60,000 miles or so. OEM is adequate.